The project involves a characterization of the recombinogenic potential of various pairs of DNA substrate molecules. Matings are done between various pairs of lacZ minus alleles and the kinetics and ultimate level of recombination are determined by assaying for the transcribable intermediate and for viable recombinant colonies. The transcribable intermediate is the wild-type protein product produced when the two mutant alleles have recombined to give a wild-type DNA nucleotide sequence. In addition to examining the ability of a lacZ minus gene to recombine as a function of its location on different types of DNA molecules, studies are being conducted regarding the recombination pathway dependence of these various combinations of DNA substrate molecules. The project also involves physical characterization of the DNA substrate molecules used in the recombination experiments. The other phase of this project involves studying the kinetics of recombination between two lacZ minus alleles in an FlacZ A/lacZB recA minus merodiploid when the cells are made Rec plus by infection with lambda precA. Recombination in this situation is measured by assaying the transcribable intermediate. The RecB dependence of this process is also being investigated.